A loop of saw chain is not elastic for the purpose of mounting it on a chain saw. The typical arrangement is for a guide bar to be mounted to have linear adjustment relative to a fixed drive sprocket. By moving the bar toward the drive sprocket, the chain can be readily mounted in a circular path around the bar and sprocket. In such condition the chain is loose and will be thrown off the bar if cutting is attempted. Thus the bar is moved away from the drive sprocket until the chain is properly tightened and at that position the bar is clamped against the chain saw housing.
The chain has to be periodically replaced. It also, from time to time, can become loosened during use and the user has to retighten it by further movement of the bar away from the drive sprocket. The tightening process is important for both performance and safety and is a significant feature of a chain saw.
Whereas typically the tightening mechanism has been provided on the chain saw housing (a threaded screw having a finger engaged with the guide bar moves the bar toward and away from the drive sprocket), such a mechanism has been a problem for users and an alternate tightening mechanism has been developed. See the disclosure of commonly owned U.S. patent application Ser. No. 08/944,933. The present invention is an improvement to this alternate mechanism and the disclosure of the above application for patent is incorporated herein by reference.